Sound dampening felt



3,002,879 SOUND DAMPENING FELT Eugene E. Johnston, Lockport, N.Y., assignor to The Patent and Licensing Corporation, New York, N.Y., a corporation of Massachusetts No Drawing. Filed Dec. 20, 1956, Ser. No. 629,441 4 Claims. (Cl. 162-135) The present invention relates to an improved sound dampening felt and more particularly to an improved felt for sound dampening of steel surfaces such as automotive bodies.

Since the introduction of all steel automotive bodies, it has been necessary to treat the steel surfaces with sound dampening materials to effectively reduce the noise level within the car. The parts of the car which may require sound dampening treatment include the roof, door panels, quarter panels, trunk lids, etc. For many years the automotive industry has generally utilized a product of dry felt saturated with asphalt after forming on a paper machine for the purpose of sound dampening. Certain areas in the car, as for example, the floor and dash require greater sound dampening and these requirements have been made by multiple felt compositions of two,

three and four layers which are laminated together by asphalt or mineral stabilized asphalt. These felt compositions are Widely used in the industry and exceed the use of any other type material.

The sound dampening or vibration dampening material is formulated so as to possess requisite physical properties to dampen or absorb the vibratory sounds of the metal part with which it is to be used. To that end the sound dampening material generally takes the form of sheets or pads of a bibulous fibrous felt, the felt being partially but substantially uniformly impregnated with bituminous material forthe purpose of imparting added mass and strength and other desirable properties thereto.

A simplified flow diagramof the process is as follows:

Belt

Filler-water fiber 7 slip Felt machine stock refining system Felt machine Dryer l Satur'etor Asphalt flux Finished saturated and filled felt More specifically illustrative thereof is a fibrous felt which in its raw, unimpregnated state weighs, say, from 11 to 14 pounds per hundred square feet, possesses a kerosene number of approximately 250, a tensile strength of approximately 16 with the grain (one inch strip), a porosity (as measured by a Gurley densonieter) less than 11 and a caliper of approximately 0.080 inch.

Typical of bituminous material with which such a felt may be readily impregnated for the purpose aforeted States Patent "ice said, is an asphalt having a softening point of approximately 70 F.; a viscosity (Saybolt Furol at 210 F.) of approximately seconds; penetration values (needle, grams, 5 seconds) of approximately at 32 F., and approximately 15 at 0 F.; and a flash point (C.O.C.) of above 500 F.

Ordinarily, in most instances, the fibrous felt of the type above-illustrated, is partially but uniformly impregnated with a bituminous material such as typified by the one above-described, to a degree such that the bituminous component will constitute approximately 30% to 50% by Weight of the impregnated felt. In any case, the thus treated felt, in order to serve efficiently as a dampening material for vibratory metal members, such as the roof or door panels of an automobile body, should exhibit a stiflness (as measured by the Olsen tester at 75 F. at 0.15 pound added weight) of less than 65 with the grain of the felt, and less than 35 across the grain; a tensile strength (two inch strip) greater than 20 with the grain and at least 10 across the grain; a porosity (measured by the Gurley densometer) less than 12; a caliper (measured by the Randall Stickney gauge with one pound added and one inch diameter circular foot) of approximately 0.0909 inch; and a cold flexibility suficient to withstand bending around a 1 /2 inch mandrel at 0 F. without delamination or cracking.

One problem which becomes important with light colored upholstery is bleeding of the bituminous material particularly at the stitching which can soil the upholstery material.

It is an object of the present invention to provide a sound dampening felt with reduced bleeding of bituminous material.

It is a further object of the present invention to provide a sound dampening felt having improved sound dampening.

It is a further object of the present invention to provide a sound dampening felt having reduced susceptibility to temperature change.

It is a further object of the present invention to provide an improved sound dampening felt having an improved absorption of saturation oils.

It is a further object of the present invention to provide an improved sound dampening felt having improved limpness.

It is a further object of the present invention to provide an improved sound dampening felt having an improved tensile strength limpness relationship.

These and other objects are attained by the present invention which relates to improved sound dampening felt comprising a bituminous impregnated dry felt containing a finely divided non-fibrous inorganic filler such as clay and/ or slate dust in the range 20-33% by weight of the dry felt before saturation.

The incorporation of this abnormally large quantity of filler in the felt is accomplished by the addition of quantities of filler in the range 50%-100% of the Weight of fiber of a dry basis, preferably as a slip in the stock refining system and preferably into the circulating water ahead of the circulating pump on the felt machine. The retention of filler in the felt is such that the 50% yields a total of 20% by weight of the finished dry felt before saturation and the 100% of filler yields about 33%.

In the manufacture of the dry felt with the 20%-63% of filler the felt was found to have an improved drying rate, improved formation, increased pliability, and increased density.

Three general types of saturation were accomplished on the improved dry felt in the customary manner to give various improved results, the first method being the preferable one. The first method involved the satura- 3 1 tion on only one side of the felt with the usual 70 -90 F. softening point asphalt flux limiting the saturation to 15 %-25 and preferably 20% by Weight of the saturated felt. This is substantially below the normal amount of saturation but yielded a product having substantially equivalent sound deadening properties with improved stain resistance. The second method involved saturation of the felt on both sides with approximately 50% of a 100-l30 F. softening point asphalt flux. While this is the normal amount of asphalt fiuxthe asphalt Was somewhat harder than usual but the product had improved sound deadening properties with improved stain resistance. The third method involved the use of very substantial amounts of saturant, i.e. in the range 60%-70% of the l-130 F. softening point asphalt flux. This felt had sound deadening values much superior to the usual felt and yielded a product quite heavy for a single ply sound deadening felt yet exhibiting the deadness necessary to the application of the felt to curved surfaces.

One specific sound deadening felt was prepared by adding a clay slip to the felt stock at the overflow of the vat at the rate of 50 lbs. per minute and adding slate dust in a slurry at the screen inlet at the rate of 50 lbs. per minute. The total filler addition amounted to 50% by Weight of the fiber. The finished dry felt had a caliper of .076", a weight of 74.3 lbs. per 480 sq. ft. and had ash content of 20.1%. This felt was saturated on one side only with 80-90 F. softening point asphalt flux. The finished sound deadening felt weighed 87.0 lbs. per 480 sq. ft. and contained 17.8% of saturating asphalt.

Where felts with high sound deadening value are made according to the present invention with the larger quan tities of asphalt the surface of the'felt may be treated further with a starch coating to inhibit staining and/or with a sodium nitrite treatment to inhibit oxidation of metal parts. The dry felt before asphalt saturation may be treated with sodium aluminate. The dry felt may also be sized with any of the usual sizing materials including asphalt emulsion.

I claim:

1. A process for producing an improved sound dampening felt adapted to be adhered to the surface of a vibratory object for dampening the vibrations thereof, comprising the step of adding finely divided non-fibrous inorganic filler in the form of a slip during the felt formation, said filler initially comprising from 50%-100% by weight of the dry fiber content of the stock in order that the dried felt may contain 20-33% by weight of the filler and saturating the felt after drying with a bituminous saturant.

2. A process for producing an improved sound dampening felt adapted to be adhered to the surface of a vibratory object for dampening the vibrations thereof, comprising the step of adding finely divided non-fibrous inorganic filler in the form of a slip during the felt formation by combining said slip with the circulating Water ahead of the circulating pump on the felt machine, said filler initially comprising from 50%-100% by weight of the dry fiber content of the stock in order that the dried felt may contain 20-33% by Weight of the filler and saturating the felt after drying with a bituminous saturant.

3. A process for producing an improved sound dampening felt adapted to be adhered to the surface of a vibratory object for dampening the vibrations thereof comprising adding finely divided non-fibrous inorganic filler in the form of a slip in the stock refining system during felt formation, said filler initially comprising from 50%-100% by weight of the dry' fiber content of the stock in order that the dried felt may contain 20-33% by weight of the filler and saturating the felt after drying with a bituminous saturant having a softening point in the range -90 F. such that the finished product contains 15 %-25 by weight of bituminous saturant.

4. A process for producing an improved sound dampcning felt adapted to be adhered to the surface of a vibratory object for dampening the vibrations thereof comprising adding finely divided non-fibrous inorganic filler in the form of a slip in the stock refining system during felt formation, said filler initially comprising from 50%-100% by weight of the dry fiber content of the stock in order that the dried felt may contain 20-33% by weight of the filler and saturating the felt after drying on one surface only with a bituminous saturant having a softening point in the range 70-90 F. such that the finished product contains 15%-25% by weight of bituminous saturant.

References Cited in the file of this patent UNITED STATES PATENTS 300,946 Carey June 24, 1884 1,663,095 Perry Mar. 20, 1928 1,772,434 Kirschbraun July 30, 1929 1,978,923 Wiener Oct. 30, 1934 2,044,281 Clark .Tune 16, 1936 2,049,469 Novak Aug. 4, 1936 2,049,978 Schur et a1. Aug. 4, 1936 2,051,168 Greider et al Aug. 18, 1936 2,067,876 Campbell Jan. 12, 1937 2,368,635 Booth Feb. 6, 1945 2,930,106 Wrotnowski Mar. 29, 1960 

1. A PROCESS FOR PRODUCING AN IMPROVED SOUND DAMPENING FELT ADAPTED TO BE ADHERED TO THE SURFACE OF A VIBRATORY OBJECT FOR DAMPENING THE VIBRATIONS THEREOF, COMPRISING THE STEP OF ADDING FINELY DIVIDED NON-FIBROUS INORGANIC FILLER IN THE FORM OF A SLIP DURING THE FELT FORMATION, SAID FILLER INITIALLY COMPRISING FROM 50%-100% BY WEIGHT OF THE DRY FIBER CONTENT OF THE STOCK IN ORDER THAT THE DRIED FELT MAY CONTAIN 20-33% BY WEIGHT OF THE FILLER AND SATURATING THE FELT AFTER DRYING WITH A BITUMINOUS SATURANT. 